Patent GB-774097-A (GB)
Title: Method and apparatus for embossing
Inventor: EWING HENRY
IPC: D06Q1/08
Filed: 1954-04-12
Abstract: 774,097. Embossing. BRITISH CELANESE, Ltd. April 7, 1955 [April 12, 1954, April 15, 1954, Nov. 16, 1954], Nos. 10289/55, 10290/55 and 33143/54. Divided out of 774,096. Class 100(2) The surface of a thermoplastic film 10 is modified by pressing it in a heated condition, in which it is readly distortable, between the surface of a travelling belt 21 and that of a rotating shell 13, the belt being urged towards the shell 13 by a roller 22 and driven from it by friction through the film. The belt is preferably a felted wool blanket but may alternatively be a patterned rubber belt. The shell 13 carries an embossing surface described below and is supported on a driving shaft 17, being located against sideways displacement by guide rollers 18, 19 and against longitudinal displacement by collars on the shaft 17. A radiant heater 20 heats the film to the softening temperature before it enters the nip betwen the belt 21 and shell 13. After emerging from the nip the film is cooled before being stripped off the surface of the shell, passed over roller 15 and wound up on a roll 16 under constant tension. The cooling may be assisted by blowing air or spraying water against the film or against the inside of the shell. The pressure applied by roller 22 is variable by adjusting weights 24 on the mounting frame 25. A pair of rollers may rtplace the single roller 22, the blanket 21 passing round these rollers and upper roller 23. In this case the blanket may be pressed against the embossing surface by a rubber belt passing round one of these rollers and the upper roller 23. The heater 20 is adjustable towards and away from the drum to allow the temperature of the web entering the nip to be exactly controlled. The thermoplastic film may consist of cellulose acetate or other esters of cellulose, cellulose ethers, e.g. ethyl cellulose, polyvinyl and polyvinylidene compounds such as copolymers of vinyl chloride and vinylidene chloride, polystyrene, blends of polystyrene or other thermoplastic synthetic resin with linear diene polymers. In most cases plasticisation is necessary to cause the film to be sufficiently heat-softening. Other materials that can be used with a more careful temperature control are polythene, nylons, polyesters such as polyethylene terephthalate and the polyurethanes. Embossing surfaces:-The surface 14 of the shell 13 may consist of a patterned fabric such as lace or a knitted fabric, either warp- or circular-knitted, or a felt. These may be stuck to the shell by means of a thermosetting cement and baked. Fabrics of wire or of mineral fibres, e.g. glass and asbestos can also be used. Circular woven or circular-knitted fabrics are very suitable since they can be slipped over the shell and cemented in place. Brushed fabrics such as surgical lint can be used and produce a fine matt effect on the film. Grains of materials such as-sand, emery, glass may be stuck to the shell or designs cut out of cardboard or sheet metal or moulded designs may be used. Patterns can otherwise be built up by metal spraying or electrodeposition or the surface of the drum may be etched, engraved or perforated. A cardboard master carrying a Braille Script may be secured to the shell and letterpress may be similarly embossed. Blotting paper or fine manilla paper may also be used as the embossing surface, the film so produced bearing an impression of the felted blanket. 21 on one side and a fine matt surface on the other. This latter surface can be used for writing on in pencil or ink, such writing being easily erased. The shell is made of copper, aluminium or where a low conductivity is required, laminates may be used composed of fibrous webs and heat-resisting bonding agents, e.g. synthetic resins.